1. Field of the Invention
The present invention relates to an exposure apparatus for forming a pattern on a semiconductor wafer, used as a substrate, by exposure in a vacuum atmosphere.
2. Description of the Related Art
In producing devices with fine patterns, such as semiconductor devices (semiconductor integrated circuits, for example), micromachines, and thin-film magnetic heads, using a mask (original plate), a desired pattern is formed on a semiconductor wafer (used as a substrate that is a transfer member) by illuminating the wafer with exposure light (exposure energy) either directly or through a projection lens (projection system). Hereafter, the term “exposure light” will be used as a general term to include visible light, ultraviolet light, extreme ultraviolet (EUV) light, X-rays, electron rays, and charged particles; and the term “projection lens” will be used as a general term to include a refractive lens, a reflective lens, a catadioptric lens, and a charged particle lens.
In producing a semiconductor device, when a mask, which is formed in correspondence with a desired circuit pattern, is provided for a semiconductor wafer with a resist coated on its surface, the circuit pattern is transferred onto the semiconductor wafer by illuminating the semiconductor wafer with exposure light through the mask and the resist is selectively exposed. After this, etching and film deposition are carried out. By repeating these steps, a desired circuit is formed on the semiconductor wafer. Even in the case in which a circuit pattern is directly formed on a semiconductor wafer without using a mask, a desired pattern is formed on the semiconductor wafer by the same steps.
An exposure apparatus that uses as exposure light extreme ultraviolet (EUV) light having an oscillation spectrum in a wavelength range of from 5 nm to 15 nm (i.e., the soft X-ray region) is disclosed in, for example, Japanese Patent Application Laid-Open No. 09-298142. (Such an exposure apparatus will hereafter be referred to as an “EUV exposure apparatus.”)
In an EUV exposure apparatus, the surrounding environment of an illumination light path from an EUV light generating source to a mask and/or an exposure light path from the mask to a wafer is in a vacuum. Hereafter, although the present invention will be described by taking the EUV exposure apparatus as an example, the present invention may also be applied to exposure apparatuses which, as in the EUV exposure apparatus, require the surrounding environment of its exposure light path to be in a vacuum and which make use of a charged-particle beam exposure such as an ion-beam exposure or an electron-beam exposure.
In the EUV exposure apparatus, a mask stage for holding a mask (or reticle), used as an original plate, and a wafer stage for holding a wafer, used as a substrate, need to be in synchronism with high precision in order to perform scanning and exposure operations. At the same time, in the EUV exposure apparatus, at least one exposure structure needs to be supported with high precision while removing and/or deadening vibration of the at least one exposure structure. The at least one exposure structure includes at least one of a projection lens (used as a projection system), a mask stage plate for supporting the mask stage, and a wafer stage plate for supporting the wafer stage.
In general, in order to remove and/or to deaden vibration, the at least one exposure structure is supported with respect to the floor (serving as a base) or a vacuum chamber (used to form a vacuum atmosphere) through, for example, a vibration absorber. The vibration absorber absorbs the vibration of the at least one exposure structure by absorbing the vibration from the floor. If necessary, the vibration absorber is provided with another function of deadening vibration to restrict vibration that is generated by the movement of the stages on the respective stage plates.
A damper or an actuator of the vibration absorber is often formed by using an air spring as a gas spring, so that there is a problem in supporting the at least one exposure structure, such as a projection lens, in a vacuum atmosphere.
One method of solving the problem referenced above is to dispose the vibration absorber at the outer side of the vacuum chamber and to support this and the at least one exposure structure in the vacuum chamber with, for example, a support by joining them with the support. However, when this method is used, an opening for passing the support through the vacuum chamber is required, thereby giving rise to a problem in that the opening must be covered in order to cut off the inside of the chamber from the outside atmosphere. In addition, this method has still another problem of the generation of a large amount of vibration due to the rigidity of the support.